This invention relates to a process for the conversion of higher allylic alcohols to allylic ethers by a coupling reaction with alkylene glycols.
The allylic ethers of interest to this invention are those produced by the coupling of higher allylic alcohols with alkylene glycols. This coupling reaction can be illustrated, for instance, by reactions of higher 2-alken-1-ols or 1-alkene-3-ols with ethylene glycol: ##STR1## wherein R is an alkyl group of from about 3 to 17 carbon atoms. The higher carbon number allylic ethers of alkylene glycols have utility as chemical intermediates. The ethers are known to be useful in the preparation of valuable polymers by polymerization either alone or with vinyl monomers (e.g., ethylene, styrene, or acrylonitrile), and can also be used in the synthesis of nonionic and anionic surfactant products.
It is generally known in the art that such allylic ethers can be prepared by reaction of allylic alcohols with one or more alkylene glycols (including polyalkylene glycols) selected from the group consisting of ethylene glycol, polyethylene glycols, propylene glycol, and polypropylene glycols. U.S. Pat. No. 3,250,813 to R. J. Stephenson, for instance, discloses a process which comprises a reaction between an allylic alcohol and itself or another alcohol in the presence of, as catalyst, a cuprous salt and, as cocatalyst, an acidic material such as a trivalent inorganic acid, a Lewis acid, a sulfonic acid, or an acid ion exchange resin. U.S. Pat. No. 3,250,814 describes a process for the preparation of allylic ethers from diallyl ethers and alcohols using the same catalyst system.
The present invention provides an improvement upon the prior art process for the preparation of higher allylic ethers from higher allylic alcohols, specifically an improvement upon the selectivity of the process for the production of allylic ethers of the alkylene and polyalkylene glycols. As expressed in the disclosures of the prior art, the allylic alcohols react only with other alcohols (and glycols) but also react with themselves. "Dimerization" reactions involving the allylic alcohol reactant (and often also the allylic ether product) are commonly the greatest factor reducing the selectivity of a process intended for the preparation of the desired allylic ethers. Both of these reactions are termed dimerization because the resulting molecule combines two of the allylic alcohol molecules. Investigations have shown that when prior art practices are applied to the reaction of the above-specified higher allylic alcohols with alkylene glycols, allylic alcohol dimer products account for as much as twenty percent of the final ether product, representing not only a loss of allylic alcohol reactant but also a source of product contamination.
Accordingly, a process improvement which increases the selectivity of the allylic alcohol reaction for the production of the alkylene glycol ethers would be highly desirable.
In one respect, the invention relates to the discovery that the presence of a certain solvent in a certain minimum quantity in the reaction mixture of the process for the preparation of allylic ethers of alkylene glycols can substantially enhance the selectivity of the desired etherification reaction. It is known in the art (for example, from the disclosure of the aforementioned U.S. Pat. No. 3,250,813) that certain of the solvents now found to be suitable for this purpose have previously been added to allylic alcohol reactions as azeotroping agents. In this respect, it has been reported that azeotroping agents may improve the process performance by removing (through evaporation) water formed in the course of etherification reactions. In the processing of higher carbon number allylic alcohols, under conditions specified for practice of this invention, however, the presence of water in the reaction mixture is not a disadvantage and there is no incentive for its azeotropic removal. Moreover, under this invention, it is necessary that the solvent remain in the reaction medium in substantial quantity throughout the course of the process. The requirement of the invention for the presence of relatively large proportions of solvent throughout the process is inconsistent with quantities of solvent reasonably employed for azeotrope formation with water and, more importantly, with the evaporation and removal of the solvent over the course of the conventional process.